In a road vehicle, especially a car, it is advantageous to be able to freely distribute drive torque to different wheels in order to enhance the driving dynamics of the vehicle. Devices for accomplishing this desired result are in the art referred to as torque vectoring devices.
Torque vectoring devices may be used in either two-wheel drive vehicles or four-wheel drive vehicles, although the latter case must be regarded as more common. It can also be used for either rear or front drive shafts or in the cardan shaft for distributing torque between the front and rear drive shafts. In the present specification the example with the rear drive shaft of a four-wheel drive vehicle has been used. The torque is here distributed between the two wheels of a rear shaft provided with a conventional, central differential.
In order to obtain the desired result with regard to the driving dynamics, it may in certain situations be advantageous to provide a drive wheel with a positive torque in relation to the other drive wheel on the drive shaft. Such a positive torque may be obtained in a way known per se by a mechanical gear device for gearing-up or increasing the rotational speed of the drive shaft for the wheel in question by for example 10%.
Many examples of such mechanical gear devices are known. In a typical arrangement torque vectoring devices are arranged at either side of the central differential for the two drive shafts. A typical example is shown in WO02007/079956. The arrangement is both expensive and heavy. It is therefore advantageous to find solutions to the problem of having one torque vectoring device at one side of the differential for the two drive shafts.
The main object of the invention is to provide such a torque vectoring device which is as cheap and light-weight as possible without in any way impairing its reliability or effectiveness.